1. Field of the Invention
The invention relates to the production of 4-alkoxy-2(5H) thiophenones.
2. Background Art
Up to now advantageous processes have been lacking for producing thiotetronic acid, especially thiotetronic acid in highly pure form, in a good yield.
From E. Benary, Chem. Berichte 46, 2103 (1913), it is known to produce thiotetronic acid, starting from acetylthioglycoyl chloride, by reaction with sodium malonic ester and subsequent ring closure and water treatment. D. B. Macierewicz, Rocz. Chem. 47, 1735 (1973), duplicated the reaction of E. Benary and in doing so obtained thiotetronic acid in a yield of 30.3 percent, in relation to the acetylthioglycoyl chloride used.
The synthesis of J. Z. Mortensen et al., Tetrahedron 27, 3839 (1971), shows another possibility. Starting from 2,4-dibromothiophene, the thiotetronic acid is obtained in a yield of 46.2 percent through three steps by reaction with butyl lithium and tert-butyl perbenzoate.
Moreover, it is known from European Patent Application No. 0189097 and the corresponding U.S. application Ser. No. 818,766, filed on Jan. 14, 1986, which was refiled on July 23, 1987, as U.S. application Ser. No. 76,855, to produce thiotetronic acid by the reaction of chloroacetoacetic acid chloride with H.sub.2 S in the presence of trimethylamine. A disadvantage of such process is that the thiotetronic acid can be produced only by an expensive extraction with inadequate quality (content 88 percent). In addition, working with gaseous H.sub.2 S in regard to an industrial process is not without problems. The pertinent parts of U.S. Ser. No. 76,855, filed on July 23, 1987, for "Process For The Production Of Thiotetronic Acid", which is a continuation of U.S. Ser. No. 818,766, filed on Jan. 14, 1986, are incorporated herein by reference.
For the production of a better thiotetronic acid quality, a process is known from European Patent Application No. 0189096 and the corresponding U.S. application Ser. No. 818,747, filed on Jan. 14, 1986, which is distinguished by the reaction of 4-chloro-4-chloromethyloxetan-2-one with hydrogen sulfide in the presence of an amine directly to the thiotetronic acid, or in a second variant by the reaction of the unisolated thiotetronic acid with ketene to 2,4-diacetoxythiophene, which for its part is reacted with a mineral acid to thiotetronic acid. A disadvantage of such process is that it is started using an deduct which is not available on a large industrial scale but which must be produced in a separate synthesis step. In addition, a pure thiotetronic acid is possible according to the first variant only after a chromatographic purification and according to the second variant only by the roundabout way of the production of the easily purified 2,4-diacetoxythiophene. Also such process, because of the use of H.sub.2 S in the industrial framework, must be evaluated as having problems associated therewith. The pertinent parts of U.S. Ser. No. 818,747, filed on Jan. 14, 1986, for "Process For The Production Of Thiotetronic Acid", are incorporated herein by reference.